Apparatus for radiotransmission



Nov. 29, 1927. 1,350,944l

ABDELRAHMAN Z. A. KHALIFAH APPARATUS FOR RADIO TRANSMISSION FiiedNov, 29,1922 'cs-sheer 1 Nov. 29, 1927. 1,650,944

ABD*ELRAHMAN Z. A. KHALIFAH APPARATUS FOR RADIO TRANSMISSION Filed Nov. 29, 1922 2 Sheets-Sheet 2 E E- E- Pos-Hon of Aerial Inducan Pos-Ninn gf Civ-zuid' fn be swcws ad when crcui @cod on through hes C httat earner ,i t? Fly C' El APPARATUS FOR RADIO'ERANSMISION.

Application. led November 29, 1,922. Serial No.604,105.

The present invention'relates to radio apparatus, and aims to provide a multiplex apparatus tor the transmission of intelligence (either telegraphically or telephonically) .ufherein there is provision tor multiple inductanccs and capacities, in order that, when used in a sending station, one or more (up 'to as many as provision is made for) receiving,` stations tuned or adjusted 'for ditierent Wave lengths can he simultaneously given the sign nais, message or other' intelligence, the send ing` or loroad-castinn` apparatus being capable oi' transmitting the information or intelligence in number of diterent Wave lengths at the time; and "thapparat;us is also useful in a receiving station in order to enable quick tuning to he obtained by the provision of themultiplc inductances and capacities, requiring no adjustments other than making circuit connections through a conrenient switch board.

There are circumstances which render it highly desirable to `enable signals, messages or other intelligence to be transmitted in dii'lierent Wave lengths simultaneously, for which the present apparatus is admirably suited.` For example, a ship in distres would be capable oit sending out distress signals in anurnher oit dirterent Wave le ff'ths in order to assure ot the signals or mesagre beine' picked up by some receiving station, either on the land or other ship`to assure ot assistance being1 received, Whereas the send ing' out of a signal or message in a single wave length might not reach ay station" although there are receiving stations Within harina' other Wave lengths of adjust! Y ln this'way, bythe transmission ot a signal or me, in a number of diilerent Wave len; hs, Aassurance ishad of the signal or message reaching,r any and all stations within ranger ha\f'ing` the given Wave lengths of adjustment. rllhe principle also useful for other purposes inasmuch as in formation or entertainment ot a public or general nature can be b1'oud-asted in i number of f liitl'erent Wave lengths so as to he simultaneously transmitted to receiving statici h ngi' different Wave lengths. instead n; the afljust ,he rece ois to a given nave length of trani-1n mission.

The underl;Y principle oil the present apr: tus in the inclusion in -the sen circ device a series ot d Cnd cerf spending' capa@ ities in succession, and'with sutlicient rapidity or speed so as not to interfere with or break up the telephonie sound 'waves or tele graphic dots and dashes, whereby the mes sage has each variation or Wave thereof split or divided up into a number of different wave lengths so as to be capable of reception by receiving apparati tuned for such different Wave lengths.

The apparatus is also of advantage in a receiving set for quick tuning, inasmuch as the different inductances and capacities are ready for instant use, it onlyT being necessary' to make suitable circuit connections to bring` in the prosper inductance and capacity :forr Vthe particular Wave length, instead oiire- (pairing1 careful and patient tuning adjustments.

The invention also involves a novel method I -cuit or device a series of diilgerent inductances and corresponding capacities in progressive succession, `fory the purpose of simultaneous transmission in different Wave lengths, or for quick tuning` in afrcceiving set.

With the foregoingand other objects in view, which Will he apparent as the invention is more fully understood, the invention resides in the apparatus and method as hereinafter described and claimed, it being understood that changesand alterations can be made in the details or' construction and arrangementvo the parts, Within the` scope of what is claimed, Without departing from the spirit of the invention.

The invention is illustrated in the accomv panying drawings, wherein: y

Figure l is a diaggiannnatical view` oj the apparatus. c

Finn 2 is a chart depicting* the successive inductances, capacities and aerial connections in the different positions of the com inutators.

Fig. 3 is a diagrammatical view showing the operating' means of the cominutators for controlling' the inductances and capacities.

, Fig'. 4l is a detail vieiv showing one et the plugs oit the switch board.

In the embodiment of 'the mutator 50, a primary Capacity commutator 5l, a secondary inductance commutator and a secondary capacity commutator 53, each ot which is constructed for making a series of circuit connections in succession. As shown, the commutators and 5l have the respective switch arms or brushes 5-l and secured on a shaft 56, while the secondary commutators 52 and 53 have the respective contact arms or brushes 57 and 5S secured on a. shaft 59. These shafts 5G and 59 are geared together or operatively connected, as at G0 (see Fig. 3), whereby the secondary commutators are operated in synchronism or timed relation with the primary commutators. ln the arrangement as shown, the contact arms of the secondary commutators make three revolutions to a single revolution of the contact arms 5-t and 55 oit the primar)v commutators, but the ratio depends on the number of contacts used in the con'imutators.

A conductor (il connects the contact arm 5l with a binding post (i2, `tor connecting the primary commutator 5t) in the transmit ting or receiving circuit or device, and the commutator 50 includes an annular series ol contact segments G3 (there being six as shown). Said segments (S23 are connected by the respective conductors (A to the aerial or antenna (35 at different points numbered (from l to (5) accordingy to the numbering of the segments (i3 as shown, whereby when the contact arm 54 engages the several segments in succession, corresponding aerial connections or changes are obtained in succession, there being six changes in the aerial connections Yfor twenty-tour dili'erent inductances and correspoiuling capacities, the apparatus as shown heilig designed for twentytour diil'erent wave lengths.

A switchboard is provided composed ot a series ot plug sockets, one for each wave length. so that there are twenty-four ot such sockets as shown, which are designated A1, B1, Cl, 131,152, F2, G2, H2, I1, .11,Kl, L1, Me, N2, oe, P2, Q1, R1, s1, T1, U2, Ve, lV?. and X2. Each socket has the pairs ot spaced contacts G6, (i7 and G8, and a plugtt) in insertable in each socket. The plug is ot insulating material and has the bridging rings or portions tor bridging or connecting the contacts ot the several pairs. These plugs can be readily inserted in the several sockets to make the proper circuit connections tor the corresponding inductances and capacities, whereby the different wave lengths are selected by the insertion ot the plugs in the corresponding sockets, it thus being possible to select the wave lengt-hs for either sending or receiving messages.

The primary commutator 50 has an annular series of contact segments 7l, one for each segment G3, to be engaged in succession by the contact arm 54, and a leader or conductor 72 is connected to each segment 'i to connect the commutator with the plug sockets of the switchboard. Each conductor 72 has branches 73, there being six conductors 72 in the arrangement as shown. and four branches 73 tor each conductor, providing twenty-four branches, one for each plugr socket. Each branch 7? is connected to one contact 66 of one pair, in order that thc segments 71 of thc commutator 5() are connected to the corresponding contacts (itl in groups. Thus. contacts (iti of the plug .sockets Al, lil, C1 and Dl (first group) are connected to the first segment 71. contacts ol' the plug sockets lf2, F2. (l2 and ll2 (second group) are connected to the second segment 7l. and

so on.

The other contacts (i6 of the plug sockets are connected in similar groups to the variable inductance device 74. which includes an inductance coil 75 having the terminals 7u for connecting it in the sending or receiving set in the usual manner. The coil 75 has the taps L1, L2, L3, L4, L5, and L6 to which thc conductors or leaders 77 are connected, and said conductors have the branches 7S. corresponding with the branches 73 ot the cond uctors 72. which are connected to those. con tacts ('u complementing the contacts of thc pairs to which the branches 73 are conncctml. whereby the insertion of a plug in any socket of one group will connect thc corrcspondimcr conductors 72 and 77, there beingr six groups of sockets and six pairs of conductors 72 and 77. In this way, the insertion of a plugr in an;v socket ot the lirst group (Al, Bl; C1 and D1) will connect the first segment 7l of the commutator 50 with the first tap Ll ot the coil 75, and the insertion of a socket in any one of the secoml group of sockets will connect the second segment 71 with the second tap L2. and so on.

rlhe inductancc device 74 includes a movable coil 79, which is mounted for rotation as shown, and which uiav7 be located wilhiu or in other inductive relation with thc coil i5. As shown. the coil 79 rotates with the contact arm 57 of the. seconden-j.' inductance comi'uutator F2. and the coil 75l has onv` terminal connected to the contact arm 57 and its other terminal connected by ther con (luctor or leader S0 with one terminal of the coil 75. The colninutator has the annular series of contacts Sl for the successive. cugagenicut of the Contact arm 57 for connecting the coils 75 and 7i) in the circuit in the dillcrcnt angular po--itions of the coil 7S) in succession. the contacts Si being designated al, 711, ci, (Il, n2, 7/2, c2 and IZB.

The contacts ot' the -onimutator connected to contacts (39 of the plug socl'cts. with the contacts of' the commutator counected in pairs, and each pair connected to one contact (3S of cach group of plug sockets. rthus, a conductor 82 is connected to the contacts al and a2, a conductor 83 is connected ill] seamos/i to the contacts oli andm, a conductor 84 is connected to the contacts cl and c2, and conductor 85 is, connected to the contacts Z1 and d2. rlhese conductors 82, 83, Se and 85 each have sii; branches 86, one for each group ofplug sockets, and' the branches oi each conductor are connected to one Contact 68 of each group 'ot sockets. rl`hus, the branches of the conductor 82 are connected to one of the contactsGS of each of the sockets ALHQ, l1, P2, Q1 and X2. The branches o1L the condi-i-ctor 83 are connected to kone Contact 68 of each of the sockets B l, @-2, J1, O2, R1 and 72. The brand-ies ol the conductor 84 are connected to contacts 68 of the sockets Cl, F2, K1, N21, Sl and V2, While the branches of the conductor S5 are connected to the conta-cts 68 of the sockets D1, E2, Ll, M2, T1 and U2. The coil 79 has tour ind'uctire positions with reference to the coil 75 determined by the engagement of the a-rm 57 with either ot the contacts al and a2, with either of the contacts b1 or Z22, with either oit the contacts c1 or C2 and With either of the contacts (1 and cl2, and in any inductive position of the coil 79 it is `connected with one plug scclet ot each group, and the coil 79A and arm 57 in moving through one-halt' ot' a revolution will result in the coil 79 being connected With all four sockets oi each group in succession. lnasmuch as the commutator 52 makes three revolutions t'or each revolution ot' the commutator 50, the arm 57 Will make one halt otra revolution While the arm 54s of the commutator .i0 moves through an arc or step equivalent to the length of a segment 63 or 71. rhus, duri-ngthe engagement et the Contact arm 54- With any oner segment 71, thereby con necting-` said vContact arm with the plug sockets ot one group, the connnutator will .onnect the inductance device Withthe sockets et such groupi-n succession, as Well as with the sockets oi' the other groups, and with the'coil 79l in different inductive positions in succession. The other contacts 68 are all connected to a common conductor 87 leading to a binding post 88 complementing the binding post G2, whereby the multiple or parallel shunt inductance connections can be connected in the sending or receiving circuit usual. The space between the binding; posts 62 and' 88 represents a Variable inducta'nce controlled by the commutatore 50 and 52, which may be connected in the sending or receiving' circuit in the usual mannerot connecting in the inductance, and the binding post 62 is also used for connecting in the aerialA 65 by Way oit' the conductors 611, segments 63, Contact arm 54, and conductor 61.

There is one condenser or capacity tor each inducta-nce, and with twenty-'four plug sockets in the switchboard, there are a similar number of condensers or capacities 90,

which are designated CM GB, Ce, CD, CE, CF,

C@ CH, Ci, CJ, CK, GL, CM, GN, Co, CP, Go, Cu, Cs, CT, CU, Gv, Cw and CX. These condensers or capacities are connected in succession with the corresponding plug socletsin a manner similar to the connections ot" the inductances with the plug` sockets, using the contacts 67 ot' said sockets. capacitycommutator 51 has an annular set ol contact seg-ments 91, there being six to cor-k respond With the. segments ot the commutator 50, and the switch arm 55 corresponds in position with the switch arm 511s to engage the segments 91 in succession in synchronisni withthe commutator 50, Each seg-ment 91 has a conductor 92 connected thereto and the conductor is connected to one Contact 67 of each pair of one group ot plug sockets, similar to the connection ot the conductors 72 with the contacts 66. rlhe capacity connections are not shown as completed With the contacts 67, but are indicated by nmnerals. The contacts 67 are numbered from, l to 4:8, and the conductor V92 oit the rst segment 91 is connected to the contacts 1, 3, 5 and 7, ot the tirst group, thereby Yconnecting',it with one contact 67 ofy each of the sockets of the first group. Similarly, the conductor1 92 of the second segment 9]; is connected tothe contacts 9, 11, 13 and 15 orto one contact `67 ot each of the sockets ot the second group, and so on. ln other Words, the conductors 92 are connected to the contacts 67 in precisely the saine manner that the conductors 72` are connected to thecont-ams 6G, the connections oi the conductors 92 with the contacts 37fbeingindicated by numerals, although acomplete connection with the plug socket Dl shown. rlhe contact arm 55. is connected by a conductor 93 with a bind-ing post 94, and a companion binding post 95 is connected byaconductor 96 with the contact arm 58 ot the vsecondaiy-capacity commuter tor `This com-mutat-or ihas the contacts afl, a-QJ/t, lf2, ol, (f2, (Zl and d'2. similar tothe contacts of the coinniutator The Contact arm Sis in the saine positionasthe arm 57 and they rotate one with the other so 'that the Contact engagements of the secondary commutatore is the same. A conductor 97 is connected to the pair ot contacts al and 0K2, a conductor 9S is connected to the pair ot contacts l and 52, a conductor 99 1s connected to the crmtacts cl and (/2 and a conductor 100 is connected to the pair et contacts d'1 and d'2, similar to the conaec A The. pr ima r y iin in tour horizontal rows, site in a row, to correspond with the four capacit)v positions oi the contact arni in cach halt' revolution thereo'l, with one capacity or condenser in each' row for each position ot' the arni fn?. The conductors QQ, fifi and 100 are siinilariy connected to the capacities or condensers olf the second, third and fourth rows above, as clearly apparent by reference to Fi l. Thus, with the arm 5S engaging either the Contact afl or aQ. the conductor Qt; is connected to the capacities of the first rou', and when the arni :'18 engages either the contact ZJl and 7)"2 the conductor fiti is connected to the cape` lities ot the second row, and so on. The capacities of each ron' are connected to one plug socket oi' cach group. Thus, the first group ot capacities ot the several rows (CA, lin. (in, and Cn) are connected to cor responding contacts (57 o'l the h'rst group ol plug sockets, the capacities CH, Cp. Cn. and C ot the second group are connected to contacts ('7 of the second group of plug sockets, and so on. More specifically, as indica ed by the numerals, the capacities are connected to those contacts G7 With, the even numbers running from 2 to 18, n'hile the conductors 92 leading from the coininutator 5l are connected to the contacts G7 with the odd ninnbers. Thus, in each position of the contact arm 55 in engagement with one segment Ol. such contactarrn is connected to contacts (37 of the corresponding group oit plug sockets. and the other contacts 67 ot such group are connected to the corresponding group of capacities, one in each row, and such capacities are connected in succession by the connnutator 53 with the conductor 96 and binding post 95.

The contact arin 5S makes one-half of a revolution, similar to the contact arin 57, for each step ot movement oi' the arm' through an are corresponding to the length ot a seglncnt 01. For example, when the arm engages the first segment 91, the binding post 94 is connected through the arm with the conductor 92 that is connected to the con tacts l, 3, 5 and 7 of the first group ot plug sockets. and the other contacts 2, Il. 6 and 8 ot said plug sockets are connected to the `tirst rapacities of the several rows, and thc contact ariu 5S in making one-halt of a revolution Will connect such tirst capacities ot the rows in succession with the binding post Vhen the arm engages the second segment Sil. the binding post 94s is connected 'with the contacts 9, ll, 13 and l5 ot the second group ot plug sockets, and the other contacts l0, l2, ist and 1G ot said second group ot sockets are connected to the corresponding second capacities of the four rows, and said second capacities are connected in succession by the contact arin 58 with the binding post 95. Thus, as the arin mores troni one segment to the other, the circuit is made through the groups of plug sockets with the groups of capacities in succession, divided into four rows or series, and the capacities in each group are connected in succession through the coininutator with the binding post 95. the arm .3S making one-halt of a. revolution while the arin engages any one nient 91.

The binding posts fliand 95 have the variable capacities connected between them in progressire fucccssion through the coniniutators 5t and 5?). and said binding posts arc connected in the sending or receiving circuit in the usual manner. The capacities or condens-ers are adjusted to correspond with thc diliierent imluctances` simultaneous inductance and capacit)7 connections being niade through the primary and sccondany connnutators.

The successive, inductauce and capacity changes are indicated in the chart (Fig. 2). Thus, in the tirst position ot the coininutators o() and 5l, with the contact arms 54 and starting at: u` and n, respectively, the arms 5i; and :75 engage the first segments 63 and 7l ot the connnutator 50 and the irst segnient 91 ot the con'imutator 51. respectively. The first point of the aerial is thus connected in circuit through the first segment (53, and the lirst segn'ient 71 is connected through thc irst group ot plug sockets (with the plugs in place) to the lirst tap L1 ot the inductance coil 75. Similarly, the arm engaging the first segment 91 will connect said arin through the first segment 91 with the contacts l, 3, 5 and 7 ol the first group ot plug sockets, and through the plugs, with the first group of capacities CA. Cn, C@ and CD of the four rows or series. Now, with the point of aerial connection at 1 on the aerial and with the connection with the inductance device at the tap L1, starting with the contact arm 57 at e on the connnutator 52, While the contact arin :il: is moving along the segments G3 and 7l, the arln .'37 will engage the contacts al. o1, c1 and di in succession. Thus, with the arin 57 engaging the contact al and the coil 79 in one angular position, the inductancc circuit extends troin the binding post (Si) through the conductor G1, arm 54, first seginent 7l, first conductor 72. first group of sockets, conductor 77, tap Li, coil 75, conductor S0, coil 79, arm 57, contact al, conductor S2, socket l and plug therein. conductor S7 and binding post S8, which is the first inductance. Then, in the second inductance, the arm 57 engages the contact bl. and the circuit leads from the coil 70 in a diti'erent angular position thereoftlnough Contact L1, conductor 83, socket Bl and plug therein t0 the binding post S8. .Vhen the arm 57 engages the contact cl. the coil 79 is connected, with the saine tap connection of the coil 75, in another position of the coil 79, With the socket C1, thereby providing a ncsa-sae sockets oi the first group, and with the aerial connection at the tiret point. Four correspondingcapacities archi-ought into the circuit at the same time that the four inductancesV are established. Thus with the arm 55 engaging theiirst segment 91, the binding post 94- is connected through the conductor 93, arin 55, tirst segment 91 and conductor 92 with the sockets oi the first group, and through the plugs in said sockets with the first group oi capacities CA, CB, C@ and CD. rlhek arm 58 engages the Contact ol when the arm 5?' engages the contact al, said arms 57 and 58 engaging' thecorresponding contacts simultaneously. "lhus, it' a plug is in the socket A1, with the arm 5S engaging the contact cl, the circuit includes the binding post 9st, conductor 93, arm 55, iirstseguir-mt 91, conductor 92, contact 'i' of socket A1, contact 8, lfirst capacity UA, contact ufl, arm 58, conductor 9G and binding post 95. lilhen the arm 58 engages the contact l then the second capacity CB is connected tlnough the plug in the corresponding soci-:et B1. TWhen the arm 5S engages the contact ci then the third capacity C@ is connected in the circuit, and when the arm engages `the Contact d'1 then the fourth capacity UD is connected in the circuit. fitter such rt'our inductances and capacities are established in succession for the lirst step ci thecoinmutators and 51, the arms54 `and 55 pass to the second segments of said eommutators. llie second point of the aerial is noW connected in the circuit through the second segment 63, and the binding post 62 is connected through the arm 5ft, second segment 63, the second group ot' pingI sockets and pings therein, and corresponding conductor' 77 with the second tap L2 of the coil 75. Thus, in the second position ot the connnutators 50 and 51 the second point ot connection with the aerial is used and the second tap ot the coil 75. Also, the arm engaging the second segment 91 of the commutator 51 Will connect the binding post 9st with the contacts 9, 11, 18 and 15 of the second group oi' plug sockets, and through the plugs the connection is made with the second group o capacities CE, CF, C@ and CH.

The operation is repeated iior the second group ot plug sockets with the second aerial, inductance and capacity' connections. llilhen the arm' 57 engages the contact cl2, the inductance circuit includes the binding post 62, conductor 61, arm `5d, second segment 71, conductor 7 2, plug socket E2 and plug therein, conductor 77', tap L2, coil 75, conductor 80, coil 7 9 in its corresponding angular position, arm 57, socket E2, conductor 87 and binding post 88. TWhen the armv 57 moves into engageniei'it with the contact c2, the position ot the coil 79 is changed, and the connection is made through the socket kF2,the second one ot thc second group. n through the other sockets and H2 oiV the second group when the arm 57 engages the contacts b2 and ft2. it the saine time that the second group of inductances are established in succession, the second group oi capacities are brought into the circuit in succession. Thus, with the arm 57 engaging the contact d2 and the arm 58 engaging the contact d2, the capacity circuit includes the contact 94, conductor 93, arm 55, second segment 91, conductor 92, contact 9 of socltet E2, plug in said socket, contact 10, capacity CE,

conductor 100, contact (V2, arm 58, conductory and binding post 95. As the arno 58 engages the cont-acts 02, 52 and 0;2 the other capacities CF, CG and UH oi: the second group are co'sirnected in the capacity circuit in succession. Thus, as the arms 5d and 55 'oi the primary ,commutatorsadvance along the segments the group changes, both in inductances and capacities, are made in succession, and for each group, the secondary commutators and 53 establish the individual inductance and capacity circuit' connections in succession ior the individual plug socket-s ot the particular group, so that contact d2, conductor 84, plug The connections are .made

mission, although the speed of rotation `must be suiiiciently high, so that the complete series ot inductance and capacity changes is made in a fraction of a telegraphic interruption oi' interval. That is, `tor each dot, dash vor space ot a telegraphic code, the complete series oi inductances and ca acities must be established at least once, and preferably'several times, andV the complete series of changes, in inductanccs and capacities must also beestablished at least once for each fraction of a sound Wave in telephonie transmission. Thereiore, the speed ot rotation of the connnutators must be correspondingly i hi gh, depending on the nature of the signals, r

ge or other intelligence being transmitted. also, by using different velocities ot rotation for. the commutatore in tele- When the improvements are used in a sending apparatus. by inserting the plugs in the different sockets ot the switchboard, each socket representing a predetermined Wave length, the signals'or message will be sent out in the corresponding wave lengths, and one or more plugs can be inserted in the sockets. lt is thus possible to transmit the same signals or messages in as many different wave lengths as there are plug sockets in the switchboard. or to select such desired wave lengths as Within the range oi the apparatus. then any one plug is inserted in a socket for a predetermined wave length, the corresponding inductauce and capacity connectious are made simultaneously through the same plug.

The apparatus is also useful in a receiving set by enabling quick tuning to be obtained, it only being necessary to insert a plug in the sockets in succession, and when the plug is inserted in the socket corresponding with the wave length being transmitted` the timing is at once established Without adjustments ot induetance and capacity.

Having thus described the invention, what is claimed as new is 2- 1. In a radio apparatus, a variable inductance device, a commutator tor making ditiiterent connections with said device in :succession, and a secondary commutator 'for mal ing different connections with said device in succession t'or each ot the aforesaid connections, said device including a part movable with the secondary cominutator Jfor obtaining ditiiercnt inductive relations for the dit'- ierent second named connections.

Q. In a radio apparatus. a variable inductance device including a circuit, coils in said circuit and having an inductive relation, means in said circuit for making different connections vfith one of said coils in succession, the other coil being movable, and means in said circuit movable with the last named coil Lfor making other connections with said coils in succession during each connection made by the first named means.

C). In a radlo apparatus, a variable inductance device including a circuit, coils in said circuit and having an inductive relation. a primary conunutator in said circuit ior making different connections with one coil in succession` and a secondary commutator in said circuit tor making different connectfons in succession with the coils during cach connection made by the primary connnutator, the other coil of said device being movable with the secondary commutator.

et. In a radio apparatus, a variable inductance device having coils in inductive relation, a primary connnutatol, a Switchboard having pairs of contacts arranged in groups, the connnutator having segments each connected to one contact of each pair of one group. the other contacts of the Several groups being connected to different points ot one ot said coils, and a secondary commutator Yt'or connecting said coils in a circuit in connection with the primary commutator, the secondary connnutator having contacts, the switchboard having other pairs of contacts arranged in groups similar to the aforesaid contacts, each of the contacts of the secondary con'nnutator being connected to one contact of one pair of each of the last named groups, and the secondary commutator being operated to make a series of changes in circuit connections for each connection through the primary commutator.

ABD-EL-RAHMAN Z. A. KHALIFAH. 

